A Field-Effect Transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor
. FETs are widely used in electronic circuits due to their high input impedance, low output impedance, and high gain
. They are also known as unipolar transistors because they involve single- carrier-type operation, meaning they can only have either electrons or holes as charge carriers
. FETs have three terminals: the source (S), the drain (D), and the gate (G)
. When a voltage is applied to the gate, it creates an electric field that either attracts or repels the charge carriers (electrons or holes) in the semiconductor material, controlling the current flow between the source and drain
. There are two main types of FETs:
- Junction Field Effect Transistor (JFET) : This type of FET uses a reverse-biased p-n junction to separate the source and drain terminals. The current flows through an active channel between these terminals, and the voltage applied between the gate and source controls the flow of electric current between the source and drain
- Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) : This type of FET uses an insulated gate that controls the device's conductivity per the voltage applied. MOSFETs can be further classified into two subtypes: enhancement-mode and depletion-mode MOSFETs
. Enhancement-mode MOSFETs have a channel that is normally off and require a positive voltage to the gate to turn it on, while depletion-mode MOSFETs have a channel that is normally on and require a negative voltage to the gate to turn it off
FETs are used in various applications, including weak-signal amplification, switching power supplies, digital circuits, and high-frequency applications
. They are fabricated onto silicon integrated circuit (IC) chips, where a single IC can contain many thousands of FETs, along with other components such as resistors, capacitors, and diodes
